The present invention relates to a catalyst structure and to the method of manufacturing the structure involving the formation of a catalyst surface on a metal substrate.
It is known to form catalytic surfaces on plates or other substrates for a wide variety of catalytic processes. Several prior art patents disclose the formation of catalyst surfaces on aluminum plates. U.S. Pat. Nos. 3,929,594 and 5,021,592 disclose aluminum substrates which have an unsealed porous anodic oxide layer on the substrate with a metal electrolytically deposited to form discrete metal islands having a root portion anchored in the pores of the oxide layer. It is disclosed that the plate can be a composite catalyst body by using a catalytically active metal to form the islands which then serves as a catalyst along with the catalytically active aluminum oxide layer on the substrate between the islands. Another prior art U.S. Pat. No. 5,693,207 discloses that islands, referred to therein as nodules, are formed from a first relatively inexpensive metal and then coated with a second more expensive catalyst metal. These prior art catalytic surfaces may exhibit dual catalytic activity considering both the catalytic metal islands or nodules and the catalytic activity of the anodic aluminum oxide layer.
An aspect of the prior art deposition of a metal onto the surface of a metal substrate is that there is little or no control on the distribution of the metal nodules which are formed. Metal substrates such as thin aluminum webs inevitably have microscopic parallel ridges which arise from the roll grind on the finishing rollers in the milling operations. The deposition of a metal on one surface of the metal web will take place along the top of the ridges on that surface rather than in the valleys as a natural result of the electrodeposition process. Continued deposition will only build up the deposits already started on the ridges with no deposition in the valleys. As a result, the nodules appear in rows corresponding to the roll grind and there is no control of the spacing and distribution of the nodules.